1. Field of the Invention
This invention relates generally to parallel rings utilized in dynamoelectric machines, and more particularly to methods and apparatus for conducting current from the coils of such dynamoelectric machines.
2. Statement of the Prior Art
Stator windings in large dynamoelectric machines such as turbine generators are disposed within generally cylindrical stator cores. The stator windings of multiphase generators include a plurality of phase zones each of which constitute a plurality of coil sides. All the coil sides in each phase zone except those constituting the terminal coil side portions are serially connected at each axial end of the stator core. The unconnected ends of the terminal coil sides constitute terminals which are radially separated from the axis of the stator core by discrete radial distances at a first axial end of the stator core.
Parallel conducting ring structures are disposed at the first axial end of the stator core and include a plurality of parallel rings in order to conduct the current generated by the turbine generator externally from such generator. Phase leads connect the coil terminals to the appropriate parallel rings, and the main leads which exit the casing structure surrounding the stator core are thereafter connected to the parallel rings.
A major problem that is associated with the refurbishment, or rewinding, of conventional turbine generators is that the particular way in which the main leads are connected to the parallel rings depends upon a direction of rotation of the turbine rotor, and upon the sequence in which the utilities wish the generated electromotive forces to peak. That is, depending upon the particular direction of rotation of the rotor (as set by the turbine), the parallel conducting ring structure must be so configured as to peak the generated electromotive forces as required by the utility. Looking at the exciter end of the dynamoelectric machine, some utilities require that the electromotive forces will reach their positive maximum values from left to right at their terminals or bushings (sometimes referred to as T1-T2-T3 or A-B-C in three-phase generators), while other utilities require that the electromotive forces will reach their positive maximum value from right to left.
Within the power generation industry, especially for turbines manufactured by the assignee of the present invention, a "standard" parallel ring connection consists of a counter-clockwise rotation of the turbine's rotor (as viewed from the exciter end of the stator core) together with a peaking of the generated electromotive forces on the main leads in a direction of from left to right (i.e., T1-T2-T3 and T4-T5-T6). An "opposite" parallel ring connection, on the other hand, consists of a counter-clockwise rotation of the turbine's rotor together with a peaking of the generated electromotive forces on the main leads in a direction of from right to left (i.e., T3-T2-T1 and T6-T5-T4).
One means of illustrating the nature of the "standard" parallel ring connections in comparison to "opposite" parallel ring connections would be to juxtapose arrows which would indicate the direction of both conditions (i.e., the direction of rotation of the turbine's rotor and the direction of the peaking of the generated electromotive forces). As viewed from the exciter end of the stator core, both arrows would be going in the same direction for the "standard" parallel ring connection, while for the "opposite" parallel ring connection the arrows would be going in opposite directions.
Of course the same conditions would apply for turbines having a clockwise rotor rotation together with a peaking of the generated electromotive forces in a direction of from right to left (also "standard"), and for turbines having a clockwise rotor rotation together with a peaking of the generated electromotive forces in a direction of from left to right (also "opposite"). It should, therefore, be understood that the term "standard" as used hereinafter will refer to the conditions in which the direction of rotation of the turbine's rotor is the same as the direction in which the generated electromotive forces peak, while the term "opposite" as used hereinafter will refer to the conditions in which the direction of rotation of the turbine's rotor is opposite the direction in which the generated electromotive forces peak.
Once the utility specifies its particular needs, which are dependent upon the particular connection of the turbine to the generator (which determines the direction of rotation of the turbine's rotor) and the desired direction in which the generated electromotive forces are to peak, manufacturers of dynamoelectric machines build the correct configuration into the machine. However, this can be disadvantageous when the machine requires refurbishment since the lead time which is required to correctly configure the machine often necessitates lengthy delays.
While the above described problem can be somewhat alleviated by designing a single, adaptable configuration for the parallel conducting ring structure which would satisfy the needs of utilities that utilize either standard or opposite parallel ring connections, a further problem is associated with the installation of such an adaptable configuration into the generator to be refurbished due to the limited access which is provided by a conventionally-sized opening in the axial end of a typical casing structure. It would also be desirable, therefore, to provide a method and apparatus for subassembling the parallel conducting ring structure such that the subassembly may be easily installed within conventionally-sized openings found in the axial end of the casing structure which surrounds the stator core.